Pneumatic tires have been built on flat cylindrical drums for many years. With the advent of tubeless tires, it became necessary to use a nonwicking finishing strip, also known as a chaffer strip, around the bead area of the tire. This nonwicking finishing strip serves the dual function of protecting the carcass reinforcement cords from damage by the rim and also to seal the tire chamber from air loss.
In a conventional tire building process, the tire is built up on a drum by first applying the air impervious liner and then applying the first ply of the carcass. The bead assembly is then set and the first ply is turned up around the bead. The second ply is then applied and turned down around the bead. The next step is to apply the nonwicking finishing strip and turn it down around the bead. The finishing strip should turn down far enough to cover the edge of the air impervious liner so as to prevent the inflation gas from contacting the reinforcing carcass ply. If the inside reinforcing carcass ply is exposed to the inflation gas, a leaker will result. A leaker is a tire which slowly loses its inflation pressure. A tire which slowly leaks into the carcass plies can cause serious problems by building up pressure at the carcass-tread interface. This pressure buildup can increase the probability of a tire throwing its tread off during service.
When using the conventional building sequence mentioned above, it is difficult to turn the nonwicking finishing strip down far enough to ensure that it overlaps the air impervious liner. The turndown edge of the nonwicking finishing strip will often wrinkle, thus, not covering completely the edge of the air impervious liner.
This problem has been alleviated in many tires by using what is called an under-cut building drum. In an under-cut drum, the bead area of the drum is smaller in diameter than the crown portion of the drum. This type of drum enables the tire builder to more easily make a larger turndown. However, when using a flat drum, the problem still exists. This invention alleviates this problem and results in a positive placement of the nonwicking strip in its desired location when built on a flat drum.